1. Field of the Invention
This invention relates to a resistance welding head, and a resistance welding apparatus and a resistance welding method, which use the resistance welding head.
2. Description of Related Art
In general, a wire harness for an automobile has adopted an electric connection box. The electric connection box contains wiring materials such as laminated bus bars or the like. The laminated bus bars constitute branch circuits in electric wiring. A plurality of bus bar blanks, which constitute electric circuits corresponding to a type of an automobile are formed by stamping a hoop material. Cutting and upset the bus bar blanks form tab terminals. The laminated bus bar is formed by interposing an insulation plate between the bus bars. The laminated bus bars are accommodated in a case.
A contact of the electric connection box is formed by welding the spots being welded between bus bars or by welding the spots being welded between the bus bar and electric wires by means of a spot welding apparatus.
Currently, circuits to be contained in the electric connection box are rapidly increasing in connection with the increase of electrical equipments to be mounted on an automobile. Accordingly, it has been required to produce branch circuits having a high density from a few parts.
Consequently, it has been known to divide the electric connection box into several sections, to design the sections in modules and to form circuits by welding conductor terminals provided between the modules.
As described above, the divided modules are joined to each other upon production of the electric connection box designed in modules. Consequently, it is necessary to join and weld free ends of the bus bars provided in the respective modules. Many spots being welded of the bus bars are juxtaposed very closely to one another. Since the bus bars are cut and set by a press operation, the bus bars are not always aligned precisely in the juxtaposing direction. On the other hand, a spot welding apparatus carries current in a pair of electrodes while clamping the spots being welded between the electrodes. If only one of the electrodes comes into contact with the spot being welded, the welded portion will deteriorate. In the case where many spots being welded are arranged in a poor alignment condition, it is necessary to position a pair of electrodes for every spot being welded, thereby lowering the working efficiency.
In view of the above problems, an object of the present invention is to provide a resistance welding head that can weld a number of spots, which may be poorly aligned, and a resistance welding apparatus and a resistance welding method that utilize the resistance welding head.
In order to overcome the above problems, the present invention is directed to a resistance welding head including a pair of holding units including a pair of electrodes that clamp spots being welded along a joining direction, the spots being welded being stationary in positions joined to each other, the electrodes being movable relative to each other between a welding position where the electrodes clamp the spots being welded and a releasing position where the electrodes release the spots being welded; and a driving mechanism for driving the pair of electrodes through the holding units between the welding position and the releasing position. The resistance welding head is characterized in that: a floating guide supports the pair of holding units floated movably along the joining direction so that the center of the distance between the opposing electrodes coincides with the joining center of the distance between joined surfaces of the spots being welded in a process in which the electrodes clamp the spots being welded; the driving mechanism is provided on one of the holding units; and the driving mechanism drives the other holding unit through the one holding unit.
According to the present invention, since the driving mechanism is provided on the one holding unit and drives the other holding unit through the one holding unit, when the other holding unit is displaced by the actuation of the driving mechanism, the one holding unit is displaced by the reaction force against the other holding unit and thus the pair of the electrodes are displaced from the releasing position to the welding position. During this displacement process, the respective electrodes come into contact with the spots being welded and then clamp them. At the time, even if the joined surfaces of the spots being welded are offset from the center of the distance between the opposing electrodes, both electrodes are floated movably along the clamping direction of the spots being welded through the floating guide by means of the reaction force against the electrode that is first brought into contact with the spots being welded. Consequently, the opposing center of the distance between the opposing electrodes coincides with the joined surfaces of the spots being welded. Since the present invention can perform such a self-centering function, both electrodes can clamp the spots being welded, which are in an equal contact condition and a precise welding can be carried out efficiently after the electrodes reach the welding position.
Another aspect of the present invention is directed to a resistance welding apparatus including a current-carrying mechanism for carrying welding current to the respective electrodes; an electrode position detecting mechanism that detects whether or not the respective electrodes clamp spots being welded; and a control device that controls the current-carrying mechanism so that the welding current can be carried to the respective electrodes when the electrode position detecting mechanism detects that the respective electrodes clamp the spots being welded.
Still another aspect of the present invention is directed to a resistance welding apparatus for welding a number of spots being welded, which are juxtaposed at equal intervals, by using a plurality of resistance welding heads described above, that includes a work holder for holding the spots being welded; a welding head assembly including a plurality of resistance welding heads disposed along the juxtaposing direction of the spots being welded; a mechanism for disposing the spots being welded between the electrodes of the resistance welding heads by driving the welding head assembly and the work holder relative to each other; and an intermittent driving mechanism for intermittently driving the resistance welding heads at a pitch between the spots being welded supplied between the electrodes by driving the welding head assembly and the work holder relative to each other. The electrodes of the resistance welding heads are spaced at a distance of an integer times a pitch of the spots being welded, and a control device that controls the intermittent driving mechanism is provided so that the electrodes of the resistance welding heads pass over the welded spots.
In the present invention, when a plurality of resistance welding heads weld a number of spots being welded, which are juxtaposed at equal intervals of distance, the respective electrodes of the resistance welding heads are disposed at intervals of the integer times the pitch of the spots being welded. When the respective resistance welding heads are driven by the intermittent driving mechanism, the respective resistance welding heads can weld the corresponding spots being welded.
Still another aspect of the present invention is directed to a resistance welding method for welding a number of spots being welded, which are juxtaposed at equal intervals of distance, including: disposing a resistance welding head having a pair of electrodes for clamping spots being welded in a manner of floating movably in a direction perpendicular to the juxtaposing direction of the spots being welded; applying to the resistance welding heads a reaction force exerted when the electrodes clamp the spots being welded; clamping the spots being welded while centering the electrodes; and starting a resistance welding step.
Still another aspect of the present invention is directed to a resistance welding method for welding a number of spots being welded, which are juxtaposed at an equal interval of distance by using a plurality of resistance welding heads described above, including: disposing the resistance welding heads at equal intervals of plural times a pitch of the spots being welded in the juxtaposing direction of the spots; resistance welding the spots being welded while intermittently driving the resistance welding heads together at the pitch of the spots; and driving the resistance welding heads so that the respective electrodes pass over the welded spots.
According to an aspect of the present invention, a resistance welding head is provided including a pair of holding units including a pair of electrodes, the holding units being movable relative to each other in a joining direction between a welding position in which the electrodes clamp together and a releasing position in which the electrodes are spaced from each other, a floating guide that supports the pair of holding units for floating movement in the joining direction between the welding position and the releasing position, a driving mechanism that drives the pair of holding units in the joining direction between the welding position and the releasing position, wherein the driving mechanism is provided on a first holding unit of the pair of the holding units and is configured to drive a second holding unit of the pair of holding units via the first holding unit. Further, the resistance welding head may include a support body including a pair of end plates opposed to each other in the joining direction, and the floating guide may further include a pair of spaced guide bars, each the guide bar extending in the joining direction between the pair of end plates, the pair of guide bars supporting the pair of holding units for floating movement in the joining direction between the welding position and the releasing position. The first and second holding units may further include a block, an electrode holder provided on a first end of the block and holding a respective electrode thereon, an electrode attachment tab provided on the block and configured to provide current flow to a respective electrode, and a slide section provided on a second end of the block and guided by the guide bars, the slide section including first and second slide bearings, each of the first and second slide bearings corresponding to one of the pair of guide bars and configured to slide thereover in the joining direction, so that the pair of holding units reciprocate smoothly over the pair of guide bars in the joining direction from the welding position to the releasing position and from the releasing position to the welding position.
According to a further aspect of the present invention, the driving mechanism may further include a bracket provided on the first holding unit, an air cylinder provided on the bracket, the air cylinder including a rod configured to reciprocate in the joining direction, a drive shaft extending through slide bearings in the pair of slide sections; the drive shaft including a first end coupled to the rod, wherein upon retraction of the rod, the drive shaft drives the second holding unit through the slide bearings in the pair of slide sections in the joining direction toward the first holding unit and reaction force produced thereby drives the first holding unit through the slide bearings in the joining direction toward the second holding unit so that the pair of holding units are driven symmetrically toward each other to the welding position. The driving mechanism may further include a driving flange provided on a distal end of the drive shaft, a pressure receiving flange slidably provided on the drive shaft, and a compression spring provided on the drive shaft between the driving flange and the pressure receiving flange, wherein upon retraction of the rod, the pressure receiving flange is driven by the driving flange through the compression spring and the second holding unit is driven in the joining direction toward the first holding unit and the reaction force produced thereby drives the first holding unit in the joining direction toward the second holding unit so that the pair of holding units are driven symmetrically toward each other to the welding position. The driving mechanism may further include a pushing flange provided on the drive shaft between the first holding unit and the second holding unit, and a pressure receiving projection provided on the second holding unit, wherein upon extension of the rod, the drive shaft extends and second holding unit is driven by the pushing flange in the joining direction away from the first holding unit and reaction force produced thereby drives the first holding unit through the slide bearings in the joining direction away from the second holding unit so that the pair of holding units are driven symmetrically toward each other to the releasing position. The driving mechanism may further include a pair of stopper pins provided on the pair of end plates, each the stopper pin extending from a respective end plate toward the holding units and limiting movement of the holding units in the joining direction to the releasing position, and a pair of compression coil springs, each the compression coil springs provided on a respective stopper pin between a respective end plate and holding unit, the pair of compression coil springs elastically holding the holding units in the welding position.
In another aspect of the present invention, the floating guide supports the pair of holding units for floating movement in the joining direction toward the welding position so that when the first and second holding units clamp together the first and second electrodes contact a pair of bus bars tabs equally for precise welding. The floating guide may support the pair of holding units for floating movement in the joining direction toward the welding position so that when the first and second holding units clamp together the first and second electrodes contact a dressing plate equally for precise polishing. Further, the resistance welding head may further include an intermittent driving mechanism that intermittently drives a plurality of resistance welding heads, the plurality of resistance welding heads being spaced from each other a distance equal to an integer times a pitch between articles to be welded, and the intermittent driving mechanism intermittently driving the plurality of resistance welding heads a distance equal to the pitch between articles to be welded; and a control means that controls the intermittent driving mechanism so that electrodes of the plurality of resistance welding heads may be driven a distance equal to an integer times the pitch of the articles to be welded and pass over the welded spots.
A further aspect of the present invention includes a method of welding using a resistance welding head, the method including providing a pair of holding units including a pair of electrodes, the holding units being movable relative to each other in a joining direction between a welding position in which the electrodes clamp together and a releasing position in which the electrodes are spaced from each other, providing a floating guide that supports the pair of holding units for floating movement in the joining direction between the welding position and the releasing position, providing a driving mechanism that drives the pair of holding units in the joining direction between the welding position and the releasing position, wherein the driving mechanism is provided on a first holding unit of the pair of the holding units and is configured to drive a second holding unit of the pair of holding units via the first holding unit, and driving the pair of holding units in the joining direction between the welding position and the releasing position while floatably guiding the pair of holding units. The method may further include supporting the pair of holding units on the pair of guide bars and floatably moving the pair of holding units in the joining direction between the welding position and the releasing position. The method may further include smoothly reciprocating the pair of holding units in the joining direction from the welding position to the releasing position and from the releasing position to the welding position. Further, the method may include driving the second holding unit in the joining direction toward the first holding unit, and thereby symmetrically driving the pair of holding units toward each other to the welding position and the driving flange driving the receiving flange through the compression spring; driving the second holding unit toward the first holding unit, thereby symmetrically driving the pair of holding units toward each other to the welding position, and the drive shaft extending and driving the second holding unit away from the first holding unit, thereby symmetrically driving the pair of holding units toward each other to the releasing position.
In a further aspect of the present invention, the method may include elastically holding the pair of holding units in the welding position when the pair of holding units are moved toward each other; self-centering the pair of electrodes about a pair of bus bar tabs, and clamping the pair of electrodes together and welding the pair of bus bar tabs. The method may further include self-centering the pair of electrodes about a dressing plate; clamping the pair of electrodes together and polishing the pair of electrodes. The method may include intermittently driving a plurality of resistance welding heads, the plurality of resistance welding heads being spaced from each other a distance equal to an integer times a pitch between articles to be welded, and the intermittent driving mechanism intermittently driving the plurality of resistance welding heads a distance equal to the pitch between articles to be welded, and controlling the intermittent driving mechanism so that electrodes of the plurality of resistance welding heads are driven a distance equal to an integer times the pitch of the articles to be welded and pass over the welded spots.